The mitral valve is a complex structure whose competence relies on the precise interaction of annulus, leaflets, chordae, papillary muscles and left ventricle (LV). Pathologic changes in any of these structures can lead to valvular insufficiency. Myxomatous leaflet/chordal degeneration, and dilated ischemic cardiomyopathy secondary to chronic post infarction ventricular remodeling are among most common mechanisms producing mitral regurgitation (MR). These two disease processes account for about 78% of all cases of MR treated surgically.
As part of the Framingham Heart Study, the prevalence of mitral valve prolapse in Framingham, Mass. was estimated at 2.4%. There was a near-even split between classic and non-classic MVP, with no significant age or sex discrimination. Based on data gathered in the United States, MVP is prevalent in 7% of autopsies. The incidence of mitral regurgitation increases with age and is a frequent clinically significant medical problem in the post MI population and patients with COPD.
The use of a catheter based percutaneous valved stent has been shown to be feasible in replacing both the human pulmonic and aortic valves. The pulmonic valve was the first to be successfully replaced by a percutaneous approach and is the furthest along in development. There are currently two aortic valve products in clinical trials and more in development. While there is a great deal of interest in replacing the mitral valve percutaneously (not least because many patients that have suffered myocardial infarction are not fit for surgical valve replacement) the anatomy and function of the mitral valve prevents direct application of the current aortic/pulmonic technology. However, there have been recent efforts towards developing mitral valve replacements that have focused on transapical valved stent implantation (see Lozonschi L, et al., Transapical mitral valved stent implantation. Ann Thorac Surg. September 2008; 86(3):745-8); “double-crown” valved stent designs (see Ma L, et al., Double-crowned valved stents for off-pump mitral valve replacement. Eur J Cardiothorac Surg. August 2005; 28(2):194-8); and, valved stent designs consisting of two disks separated by a cylinder (see Boudjemline Y, et al., Steps toward the percutaneous replacement of atrioventricular valves an experimental study. J Am Coll Cardiol. Jul. 19, 2005; 46(2):360-5).
It has presently been discovered that a successful percutaneously placed valve requires four major design characteristics. The valve must be compatible with acceptable delivery modalities, it must anchor to the valvular ring and seal the anchor point to prevent leaks, and the valve must function normally when in place. Among publicly available designs, there does not presently exist a percutaneous valved stent having the characteristics that are believed to be necessary for successful implantation, stability, and long-term functionality. A design having such characteristics would have profound medical implications both for those newly in need of valve replacement, and among patients that are currently fitted with conventional valve designs.